1. Field of the Invention
The present invention relates to apparatus and methods for reconditioning secondary sources of power and, more particularly, to a spacecraft secondary source having only a single battery that includes multiple packs such that one pack can be reconditioned while the remaining packs are operable.
2. Description of Related Art
Terrestrial and non-terrestrial vehicles that are solar powered typically include a secondary source of power that is available when solar power is unavailable. In particular, satellites and other space vehicles normally include an array of solar cells that convert solar energy to electrical energy and provide the primary source of power for operating the various onboard electrical loads. Rechargeable batteries are provided as a secondary source of electrical power when solar energy is not available or is insufficient. Thus, the solar cells provide electrical power during the sunlight portions of an orbit while the rechargeable batteries provide power during the dark portions of an orbit. These dark portions can be significant, particularly for a low earth orbit (LEO) where there is an eclipse almost every orbit.
Having the capability to perform battery reconditioning (i.e., deep discharging and recharging) is important to minimize risk of a battery failure before completion of the space vehicle design life. Reconditioning is also used to understand battery state-of-health so satellite operators are not surprised with a failing battery. Because of battery stresses characteristic of LEO operations, essentially all space vehicles flying in LEO have the capability to perform battery reconditioning. There are some LEO space vehicles that, because of mission constraints, must have battery availability for space vehicle operations such that there is no opportunity to take a battery off-line to perform reconditioning and still support mission operations.
Space vehicles have been designed with more than one battery to achieve battery reconditioning capability and LEO operation. One battery can then be taken off-line for reconditioning while the remaining batteries provide power. As an example, U.S. Pat. No. 3,997,830 discloses each battery reconditioned in sequence so that part of the secondary energy storage capacity is always maintained online for power demands that might occur during the reconditioning process. The individual cells of a battery are discharged simultaneously by connecting resistors across the cell. The terminal voltage of the battery being reconditioned is monitored and when a predetermined low level is reached the battery is connected to the solar array through battery charging circuitry and recharged. A major drawback to the multiple battery design is that the additional battery or batteries and associated charge and discharge electronics represents a significant weight and cost penalty.
A single battery that provides a secondary source of power for spacecraft electrical loads is shown in U.S. Pat. No. 5,488,282, assigned to the assignee of the present invention. The battery includes serially connected packs each including serially connected cells. Reconditioning resistors are connected across the individual packs through switches to discharge the packs when reconditioning is needed. After a pack is discharged, its reconditioning resistor is disconnected and all packs are simultaneously recharged. Each pack is sequentially reconditioned. While providing advantages, the design does not allow one pack to be reconditioned while the remaining packs provide power.
As can be seen, there is a need for an improved reconditionable battery having multiple packs. A reconditionable battery and method of reconditioning is needed wherein one pack can be reconditioned while the remaining packs are left on-line to provide current to a load. Another need is for a reconditionable battery and method of reconditioning that is low in cost and simple in manufacturing. A further need is for a reconditionable battery and method of reconditioning that is effective for space vehicles, particularly ones in LEO.
In one aspect of the present invention, a method of reconditioning a battery having a plurality of cells in a plurality of packs comprises electrically connecting the plurality of packs in series; bypassing a current produced by the battery around one of the packs; discharging the one pack; passing the current from at least another of the packs to an electrical load while discharging the one pack; and recharging the one pack.
In another aspect of the present invention, a method of reconditioning a battery having a plurality of cells in a plurality of packs in series comprises electrically connecting the plurality of cells in series; electrically isolating one of the cells; bypassing a current produced by the battery around the one cell; discharging the one cell; and recharging the one cell.
In yet another aspect of the present invention, a method of powering a space vehicle comprises generating power from solar cells when the vehicle receives sunlight; and generating power from a single battery when the vehicle cannot receive sunlight, with the battery including a plurality of packs in series; an isolation circuit associated with at least one of the packs; a bypass circuit associated with the one pack; and a reconditioning circuit associated with the one pack.
More particularly, the present invention allows a terrestrial or non-terrestrial vehicle, for example, with a single battery to perform battery reconditioning. In a non-terrestrial vehicle or space vehicle, the present invention allows operation (and in any orbit in the case of a space vehicle) with the ability to perform battery reconditioning. The single battery is composed of separate packs in series. An isolation relay circuit is between each pack and allows each pack to be isolated from the other packs. A bypass circuit across the isolated pack allows for current flow around the isolated pack, providing continued operation of the battery for support of mission operations. The isolated battery pack is then reconditioned using reconditioning circuitry while leaving enough battery capacity online to support the vehicle mission. Each battery pack is sequentially reconditioned until the entire battery has been reconditioned. The present invention is tolerant of a single failure.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description, and claims.